The adjustment of lamps for microscope illumination takes place usually in accordance with classical adjustment criteria which ensure a homogeneous illumination of the object field. This applies to the first adjustment of a microscope as well as to an exchange of a lamp. A first adjustment criterion is a sharp imaging of the light source, that is, of the light arc or of the lamp filament into the pupil of the objective. This adjustment criterion can be checked with the aid of a so-called Bertrand lens which images the objective pupil in the viewing field of the microscope. In lieu of a visual control of the sharp imaging, a CCD camera can be mounted in the image plane of the Bertrand lens and the image of the CCD camera is evaluated as to a sharpness of imaging. As a second criterion, the illumination in the object field itself can be checked as to homogeneity and, if necessary, the lamp is readjusted to maximum homogeneity. The object of lamp adjustment is to always ensure a substantially homogeneous illumination in the object field.
Because of the complexity of these classical methods for lamp adjustment, these methods are suited only to a limited extent to an automatization (in the first assembly and also after an exchange of lamps) in such a manner that the microscope ensures a homogeneous illumination of the object field without manual intervention. On the other hand, experience has shown that especially routine users of microscopes are often unable to make a lamp adjustment in accordance with classical adjustment criteria.
Beam homogenizers are used in illuminating devices for microlithographic apparatus and these illuminating devices ensure a homogeneous illumination of the mask to be imaged. Additionally, the position of the light source relative to the illuminating beam path is adjusted to maximum light power of the beam homogenizer so that the light power emitted by the light source is optimally utilized.
It would be conceivable to utilize beam homogenizers also for microscope illumination, for example, in the form of so-called fly-eye lenses or glass rods for mixing light. A homogeneous illumination of the object field would thereby be guaranteed independently of the positioning of the lamp relative to the illuminating beam path so that one could do completely without a lamp adjustment. The use of such beam homogenizers would, however, lead to a complexity in microscopes which could not be realized.